the three phrases " government-in-waiting , government-in-exile and shadow government" have more or less the same connotation:
a government that remains (in waiting) with the intent to take control of the government in response to some event as soon as possible.
so all of them are generally called
حكومة مرتقِبة/مترقبة
But if the context as I see gives the three of them separately, it is better to give each of them its own version.
So

government-in-waiting حكومة مرتقبة/مترقبة
government-in-exile حكومة في المنفى/المنفى/بالمنفى
Shadow government حكومة ظل

Regards